Question

Complex which is formed during the estimation of hardness of water is:

• A. $\left[Ca\right(S{O}_4{)}_2{]}^{2-}$
• B. $\left[Ca\right(HC{O}_3{)}_6{]}^{4-}$
• C. $\left[Ca\right(EDTA){]}^{2-}$
• D. $N{a}_2\left[C{a}_2\right(P{O}_3{)}_6]$

Answer 1

The correct option is C $\left[Ca\right(EDTA){]}^{2-}$

Hardness of water is because of presence of chloride and sulphates of calcium and magnesium. Thus for estimation of hardness, EDTA is added in presence of EBT indication.

On addition of EDTA, $C{a}^{2+}$ or $M{g}^{2+}$ form complex with EDTA, and hardness is removed by formation of $C{a}^{2+}[EDTA{]}^{4-}$ complex because $C{a}^{2+}[EDTA{]}^{4-}$ complex is most stable.

$\left[Ca\right[EDTA]{]}^{2-}$